1. Field of the Invention
The present invention relates to a document carrier sheet, for example, to a document carrier sheet applied to a document feed type scanner.
2. Description of the Related Art
In a document feed type scanner (which is an example of a read device of an optical character recognition apparatus), documents are irradiated with light when they are being fed, and the light reflected by them is received by an image sensor after passing through an optical system. Image information is obtained by the image sensor.
Where the documents are thin paper or carbon paper, the document feed type scanner is likely to feed two documents simultaneously or may cause a paper jam, and therefore does not ensure a reliable feed operation at all times. In an effort to solve this problem, a document carrier sheet is used, and the thin paper or carbon paper is inserted in the document carrier sheet.
The document carrier sheet is made up of: a base sheet serving as a support sheet on which documents are supported; and a transparent sheet which is laid over the base sheet and adhered to it at a forward end portion as viewed in the feed direction and at both side portions as viewed in the direction orthogonal to the feed direction.
In general, an image processing apparatus starts recognition processing by detecting edges of a document or the entirety of that document.
In the conventional art, however, the base sheet of the document carrier sheet is white. In other words, the background of documents is white, the same color as the documents themselves. Since the edges of the documents are therefore hard to detect, the conventional document carrier sheet is not suitable for use in an image processing apparatus.
In addition, the transparent sheet is adhered to the base sheet at the forward end portion and at both side portions. With this structure, documents that are larger than the base sheet cannot be fed, and the use of the document carrier sheet is not suitable for the recognition performed by the image processing apparatus.
In ordinary cases, a number of document carrier sheets are set in the sheet takeout section of a scanner and are taken out one by one from the sheet takeout section. After being taken out, the document carrier sheets are checked with respect to their thicknesses so as to detect whether or not two document carrier sheets have been fed simultaneously.
Each document carrier sheet holding a document is in three layers (namely, the base sheet, the document, and the transparent sheet), and in this state it is transported and subjected to thickness sensing. It is therefore hard for the thickness sensor to accurately sense the thicknesses.